Set a random visitor ID at each requests instead of using 0000000… for anonymous analytics about smooth-app

[monsieurtanuki]

@monsieurtanuki your solution is smart and seems perfect :-)

With such an enthusiastic comment I was somehow forced to code it today 😉

[alexgarel]

@monsieurtanuki because it will take time to deploy this fix to every one, I am manually patching matomo to do the same.

[monsieurtanuki]

Do not define user id (uid) for anonymous stats and instead use a random visitor id that change on every requests.

I didn't follow everything regarding matomo but it looks like we put the same value for conceptually different IDs: the visitor ID (e.g. the device id) and the visitor user ID (e.g. the user email).

I assume that what is bothering you is the visitor ID, that uses one single bucket ('0') for all non-consenting users on the server side.
It also look like you're not supposed to change the visitor ID.
A quick fix would be to compute a random letter, to store it locally, and to reuse it as the start of the visitor ID (right-padded with 0s) when the user is not consenting. Dividing the world of non-consenting users in 26 evenly distributed regions.
@alexgarel What do you think of that?

Food for thoughts:

cf. matomo.dart:

  /// The [visitorId] should have a length of 16 characters otherwise an
  /// [ArgumentError] will be thrown. This parameter corresponds with the
  /// `_id` and should not be confused with the user id `uid`. See the
  /// [Visitor] class for additional remarks. It is recommended to leave this
  /// to `null` to use an automatically generated id.

cf. visitor.dart:

  /// The unique visitor ID, must be a 16 characters hexadecimal string.
  ///
  /// Corresponds with `_id`.
  ///
  /// Every unique visitor must be assigned a different ID and this ID must not
  /// change after it is assigned. If this value is not set Matomo will still
  /// track visits, but the unique visitors metric might be less accurate.
  ///
  /// Think of this as a device ID; in case of website tracking (where Matomo
  /// originates), this would be the cookie identifying the browser and not
  /// necessarily a user (since a single browser might be used by multiple
  /// users).
  final String? id;

  /// The [User ID](https://matomo.org/guide/reports/user-ids/) is any non-empty
  /// unique string identifying the user (such as an email address or an
  /// username).
  ///
  /// Corresponds with `uid`.
  final String? uid;

[alexgarel]

@monsieurtanuki your solution is smart and seems perfect :-)